The sand piles support the shape of the leaf, making it flatter or creating some depth to hold water. The concrete is pretty thick and will stay where you put it pretty well. When we placed the concrete over the leaf we tried to keep it to the edges of the leaf and not have it extend too far beyond. Once the concrete has hardened up some the leaf will peal right off and you can use a metal file or grinder to finish the edges. How long you need to let the piece dry depends on the size and thickness of the piece a much smaller lighter piece wouldn't take as long as mine it. I think we let ours harden for 3 days.
I am sure that there are instructions to be found but we didn't really follow any. Mostly we asked questions of people that have done other projects to see how they did theirs. This was our first attempt at something like this but Ric does have concrete experience. Really it was pretty simple to do just needed some thought about how to do it.
